Engine valve actuation system

Abstract

A valve actuation system is provided. The system has an engine valve moveable between a first position at which the engine valve prevents a flow of fluid relative to the engine valve and a second position at which fluid flows relative to the engine valve. The system also has a first cam adapted to move the engine valve from the first position to the second position during a first lift period in response to a rotation of the first cam. The system has a second cam adapted to move the engine valve from the first position to the second position during a second lift period in response to a rotation of the second cam. The system also has a cam following assembly disposed between the first and second cams and the engine valve. The cam following assembly is adapted to selectively connect one of the first and second cams with the engine valve to thereby move the engine valve through one of the first and second lift periods.

Description

TECHNICAL FIELD[0001]The present invention is directed to a system and method for actuating an engine valve and, more particularly, to a variable engine valve actuation system.BACKGROUND[0002]The operation of an internal combustion engine such as, for example, a diesel, gasoline, or natural gas engine, may cause the generation of undesirable emissions. These emissions, which may include particulates and oxides of nitrogen (NOx), are generated when fuel is combusted in a combustion chamber of the engine. An exhaust stroke of the engine piston forces exhaust gas, which may include these emissions, from the engine. If no emission reduction measures are in place, these undesirable emissions will eventually be exhausted to the environment.[0003]Research is currently being directed towards decreasing the amount of undesirable emissions that are exhausted to the environment during the operation of the engine. It is expected that improved engine design and improved control over engine opera...

AI Technical Summary

Problems solved by technology

The operation of an internal combustion engine such as, for example, a diesel, gasoline, or natural gas engine, may cause the generation of undesirable emissions.

If no emission reduction measures are in place, these undesirable emissions will eventually be exhausted to the environment.

Unfortunately, the implementation of these emission reduction approaches typically results in a decrease in the overall efficiency of the engine.

However, while valve actuation timing adjustments may provide efficiency benefits, these actuation timing adjustments may also result in detrimental engine performance under certain operating conditions.

For example, a late intake Miller cycle may be inefficient when the engine is starting, operating under cold conditions, or experiencing a transient condition such as a sudden increase in engine load.

This detrimental engine performance is caused by a decrease in the mass of air flowing through the engine.

Especially under cold ambient conditions, the delayed start of compression may lead to cylinder temperatures insufficient to support good combustion and startability.

Because the shape of the cam is fixed, this type of arrangement is inflexible and may only be changed during the operation of the engine through the use of complex mechanical mechanisms.

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